Elevator systems have proven useful for carrying passengers or cargo between various levels of a building. The machine that is responsible for the movement and position of the elevator car is typically traction based or hydraulic. In the case of hydraulic elevators, controlling pressurized fluid (e.g., oil) achieves desired elevator car movement and position. The machine or drive controller operates a pump and valve assembly to control fluid flow and elevator car movement or position.
Most valve assemblies are set during system installation to achieve intended performance under expected or typical conditions. Temperature is one factor that affects fluid flow and that varies over the life of the elevator system. For example, the viscosity of the oil may vary at different temperatures. When the viscosity of the oil differs, the results of the preset valve assembly can vary. For example, under some temperature conditions it may not be possible to achieve a desired or target stopping position of the elevator car at a landing because the valve response is faster or slower than expected. While leveling techniques can be used to adjust the car position at the landing it is better to have the car stop at the intended position initially.
One approach to handling variations in fluid behavior in a hydraulic elevator system includes monitoring a flow rate of the fluid to compensate for changes in oil viscosity. U.S. Pat. No. 9,457,986 describes one such approach. While monitoring flow rate may be useful it does not address any other potential sources of inaccuracy in elevator car control. Additionally, the additional or new components needed for monitoring flow rate and controlling the machine based on flow rate information introduces additional cost and complexity into the elevator system.